PROJECT SUMMARY/ABSTRACT Clinical imaging studies in patients with obsessive compulsive disorder (OCD) have 1) highlighted the importance of the prefrontal cortex (PFC) in the pathophysiology and treatment of OCD, and 2) demonstrated marked dissociations in PFC neural activity changes associated with different elements of the disorder. Specifically, PFC hyperactivity is typically observed during symptom provocation, while hypoactivity is observed during cognitive testing. Devising interventional treatment strategies is therefore a challenge because it is unclear if PFC activity should be increased or decreased for therapeutic efficacy. In human studies, it is not possible to dissect the potential neural substrates for these state-dependent differences in PFC activity. Because in vivo calcium imaging in awake behaving mice allows tracking of neural activity in individual neurons across time and across different behavioral paradigms, we can now use this technique in preclinical models to determine whether discrete populations of PFC neurons show neural activity changes associated with symptom provocation versus cognitive impairment in OCD. To date, mouse models have provided substantial mechanistic insight into striatal dysfunction during OCD-relevant compulsive grooming, a parallel of symptom provocation. In contrast, although OCD patients reliably show changes in PFC-dependent neurocognitive domains, there have been no studies testing higher order cognition using translational paradigms in these models. To address this gap, we recently demonstrated that SAPAP3 KOs, the most widely used and well-validated OCD mouse model, show OCD-relevant cognitive impairments in a reversal learning paradigm, in addition to the previously described compulsive grooming phenotype. This preclinical model therefore provides us with the first opportunity to identify the neural activity patterns associated with OCD-relevant compulsive grooming vs. cognitive impairments in individual PFC neurons, providing a parallel to human fMRI studies performed during symptom provocation vs neurocognitive testing. Using miniature microendoscopes to perform in vivo calcium imaging in freely-moving mice, Aim 1 will compare neural activity during reversal learning and compulsive grooming in the lOFC, an area that is critical for reversal learning but which shows hypoactivity in OCD patients during task performance. Aim 2 will compare neural activity across reversal learning and compulsive grooming paradigms in mPFC. Although mPFC is not classically associated with reversal learning in wild-type mice, our preliminary data indicate that SAPAP3 KOs that successfully acquire reversal learning have compensatory activity in mPFC. Completion of these studies will allow us to determine whether non-overlapping ensembles of neurons show hyperactivity during compulsive grooming and hypoactivity during cognitive testing, suggesting discrete inputs or outputs that could be modulated with targeted brain stimulation.